linux-kernel - Re: 2.6.33-rc2: Xen/Guest switching to user mode with no user page tables

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Date:	Sun, 10 Jan 2010 14:05:35 +0000
From:	Ian Campbell <ijc@...lion.org.uk>
To:	Cyrill Gorcunov <gorcunov@...il.com>
Cc:	Brian Gerst <brgerst@...il.com>,
	Christian Kujau <lists@...dbynature.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: 2.6.33-rc2: Xen/Guest switching to user mode with no user page
 tables

On Sun, 2010-01-10 at 16:49 +0300, Cyrill Gorcunov wrote:
> On Sun, Jan 10, 2010 at 04:36:28PM +0300, Cyrill Gorcunov wrote:
> ...
> > > 
> > > With just the CS RPL fix below I see a GPF at kernel_thread_helper with
> > > SS=3 (hence my hypothesis about NULL selectors and non-zero RPL above).
> > > With both the SS and CS fixes things work fine.
> > 
> > any of CS,SS loaded with NULL descriptor should lead to #GP
> > 
> 
> though SS with RPL=0 is allowed to be NULL descriptor in 64bit mode

yes, that's what I meant.

Ian.

-- 
Ian Campbell

Tussman's Law:
	Nothing is as inevitable as a mistake whose time has come.

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